is one piece episode 791 filler?

The Sanji Retrieval Team watches in excitement as the Shark Submerge III comes out of the Thousand Sunny's third dock. Inside it are Pedro and Brook, ready to sneak in and retrieve Big Mom's Road Poneglyph.

Pedro apologizes for having to take Brook on the mission as well, but the Straw Hats do not mind and Brook says that he is good at sneaking. The duo then go underwater and sail through a river leading into Whole Cake Island.